Nonisocyanate polyurethane materials differ completely, both in structure and in properties, from polyurethanes produced from isocyanate containing oligomers and/or starting materials.
Prior art methods of producing polyurethane compounds that rely upon the reaction of terminated hydroxyl groups with terminated isocyanate groups requires the use of toxic starting materials such as isocyanates and competing side-reactions during production generates gases that result in an undesirable highly porous material. Furthermore, polyurethanes derived from isocyanates have hydrolytically unstable chemical bond rendering them highly susceptible to environmental degradation.
These problems can be overcome by making of a polyurethane without the use of toxic isocyanates, thus creating a modified polyurethane with lower permeability and increased chemical resistance properties to aqueous solutions of acids and alkalis.
We previously discovered and disclosed in U.S. Pat. No. 6,120,905 to Figovsky, the structure of hybrid nonisocyanate polyurethane network polymers, composite formed therefrom, and their synthesis. These polyurethanes are formed by a reaction of cyclocarbonates with primary amine polyfunctional oligomers. Our prior patented process carries out the cyclocarbonate-oligomer synthesis in thin film reactor at a temperature of 65 to 105° C., and at the pressure of about 6.0 to 8.5 atm for about 190 to 330 minutes. The resultant product contains not only terminated cyclocarbonate-groups but also terminated epoxy groups. We have subsequently found this process to have a very small capacity and yields cyclocarbonate-oligomer with yellow color, which is not suitable for use with clear coats and other products requiring a clear or white color.
Urethane oligomers can be prepared, as shown in U.S. Pat. No. 5,175,231 to Rappoport et al., by reacting a compound containing a plurality of cyclocarbonate groups with a diamine where the amine groups have different reactivities with cyclocarbonate, so as to form urethane oligomer with amine terminated groups. The amino-oligomer is used as a hardener of epoxy resin and can be cross-linked by reacting it with an epoxy resin to form a network structure. The cyclocarbonates are synthesized from epoxy resins and carbon dioxide in the presence of catalyst in a reactor under pressure 130-150 psi (8.9-10.3 bar) and elevated temperature 240° F. (150° C.). In the Rappoport et al. process, carbon dioxide is introduced in the bottom of the reactor previously loaded with epoxy compound and catalyst. The conversion of epoxy groups to cyclocarbonate groups is strongly dependent upon the saturation of the epoxy compound by the carbon dioxide. In the Rappoport et al process, despite vigorous stirring that generates a foam, the reaction still takes several hours and requires the use of high temperatures, high pressures, large amounts of catalyst and long reaction times, to avoid having a significant amount of unreacted epoxy groups that reduce the concentration of the urethane groups and the number of hydrogenated links in the final polyurethane network. Unfortunately, although Rappoport et al. are able to ensure that nearly all the epoxy groups have been turned into cyclocarbonate groups in this reaction, they also end up producing undesirable side reactions and products, while being more expensive and time-consuming.
Other efforts to create such nonisocyanate polyurethanes have had further problems. U.S. Pat. No. 4,758,615 to Engel Dieter, et al. discloses the process of synthesis of polymers containing nonisocyanate urethane groups by reacting polyamino compounds with polycarbonates and reacting the reaction product further with polycarboxylic acids for preparing aqueous polymer dispersions.
Production of other nonisocyanate polyurethanes based on the reaction between the oligomeric bifunctional cyclocarbonate oligomers and amines are disclosed by U.S. Pat. No. 5,340,889 to Crawford et al. In this process, liquid hydroxyurethane products are prepared by reacting a molar excess of bis-carbonate of a bis-glycidyl ether of neopentyl glycol or 1,4-cyclo-hexanedimenthanol with polyoxyalkylenediamine. However, the resultant polyurethanes lack a cross-linked network structure, and thus are not chemically resistant and also are not suitable for construction and structural materials.
The reaction of cyclocarbonates with amine compounds can result in products other than polyurethanes. For example, USSR Inventors Certificate No. 1353792 to Danilova, et al. discloses reacting an epoxy-cyclocarbonate resin, urea formaldehyde, triazine resin and amine hardener to prepare an adhesive composition. And U.S. Pat. No. 4,585,566 to Wollenberg discloses the process of synthesis of dispersants by reaction of a primary or secondary amino group with mono-cyclic carbonate.
The tensile strength and deformation properties of nonisocyante polyurethanes are comparable with standard isocyanate polyurethanes, but the nonisocyanate polyurethanes do not have pores, and thus are not sensitive to moisture in the surrounding environment. The main properties of nonisocyanate polyurethanes depend on the structure and the functionality of the cyclocarbonate and amine oligomers from which it is made.
As noted above, the known reactions for preparing nonisocyanate polyurethanes by using cyclocarbonates and primary amines are problematic in that the reaction stops before the process is completed resulting in an incompletely hardened network polymer that adversely affects the properties of network polymer. Although attempts have been made to prepare and add hardeners for epoxy resin, such as shown in U.S. Pat. No. 5,175,231, they have not is been successful in increasing the desirable properties of the nonisocyanate polyurethanes.
The preparation of cyclocarbonates has also been fraught with difficulties and products unsuitable for use in further processing into nonisocyanate polyurethanes. For example the process disclosed in U.S. Pat. No. 5,817,838 to Gründler et al. prepares cyclocarbonates from epoxides and carbon dioxide in the presence of a quanternary ammonium or phosphonium salt with a further silver salt catalyst to assist the reaction process. However, the use of the silver salt catalyst results in a material that is unacceptably dark in color.
Other processes for the preparation of cyclocarbonates require the use of high reactor temperatures despite the use of various types of catalysts. For example, U.S. Pat. No. 5,153,333 uses quaternary phosphonium compounds as a catalyst, but still requires reactor temperatures of 200° C. U.S. Pat. No. 4,835,289 uses alkali iodides and reactor temperatures of 180° C.